Light emitting diodes (LEDs) consume less power and can have a long life, and thus the demand for LEDs has steadily increased as eco-friendly products. LEDs have been used in various electronic products and recently have been used as a light source for tubular fluorescent lights for home lamps.
When a LED is used as the light source of a lamp, heat generated from the LED should be effectively transferred to the exterior of the lamp because the LED diffuses a large amount of heat.
FIG. 1 illustrates a traditional general tubular LED lamp. The housing of the lamp can be prepared by assembling a hemispherical heat radiation section and a hemispherical light transmission section, and a LED device and power supply, respectively, can be installed as the light source inside the housing.
Generally, the heat radiation section of the LED lamp housing may be prepared by die-casting a metal material having excellent heat conductivity, such as aluminum. However, there can be problems associated with this process, such as high manufacturing costs and low productivity.
In addition, if the heat radiation section is prepared with metal materials, the weight of LED lamp can increase due to the weight of the metal materials. This can render the LED lamp unsuitable as a home lamp.
The heat radiation section and the light transmission section can also be assembled by mechanical fastening methods. This, however, can increase the likelihood of LED lamp malfunction due to penetration of moisture or/and water through the crack between connections.
In addition, the heat radiation section and the light transmission section can be separately prepared and then assembled by a mechanical fastening method. This, however, reduce efficiency.
Thus, there is increased interest in heat conductive resin compositions which can replace metal materials used for traditional heat radiation sections.
It is generally known that heat can be transferred over a sort of acoustic particles called phonons. Phonons can be transferred through a medium having a crystalline structure because the phonon has properties of a sound wave. Thus, in a heat conductive resin composition, phonons may be easily and quickly transferred through heat conductive filler with a crystalline lattice. In contrast, it can be difficult for phonons to transfer through a polymer resin which has a low degree of crystallization and low heat conductivity. Also scattering can occur due to the phonons having the properties of a sound wave, so a significant amount of phonons can be lost at the interface of heat conductive filler and polymer resin. Thus, in the case of conventional heat conductive resin compositions, heat may not be easily transferred through the polymer resin having low heat conductivity, and the ease and/or rate of heat transfer can depend on the heat conductive filler having high heat conductivity.
Examples of a heat conductive filler impregnated with the heat conductive resin composition can include carbon fillers such as carbon fibers, carbon nanotubes, carbon nanofibers, graphite, and the like, and metal powders.
A heat conductive resin composition comprising carbon fillers and metal powders can exhibit electrical conductivity because the carbon fillers and metal powders can have not only high heat conductivity but also high electrical conductivity. Thus, carbon fillers and metal powders can be difficult to use in products requiring insulating properties in addition to high heat conductivity, such as a heat radiation section of a LED lamp housing.
Ceramic fillers can be used as heat conductive insulating fillers which do not conduct electricity. Because ceramic fillers have low heat conductivity, however, large amounts of ceramic fillers are typically required to prepare an insulating resin composition having high heat conductivity. If the amount of filler is increased, however, the viscosity of the resin composition can be high, which can deteriorate extrusion moldability and injection processablity. Thus it can be difficult to prepare a product using a resin composition including ceramic fillers. Also, mechanical strength of the product can be deteriorated.
Therefore, in order to prepare a heat conductive insulating resin composition having heat conductivity, electrical insulation and excellent mechanical properties, an electrical insulating filler should be used in as small amount as possible, and an effective heat conduction network between heat conductive insulation fillers should be formed.